Military Frequently Asked Questions

Question: What is the lead wire material and finish on leaded military ceramic capacitors?
Answer: Leaded military (MIL-PRF-123, MIL-PRF-39014, MIL-PRF-20) ceramic capacitors are supplied with solder-coated leads as follows:

• Axial - Copper clad steel with hot dip in 60Sn/40Pb solder.
• Radial - Copper with hot dip in 60Sn/40Pb solder.

Note:  MIL-C-11015 leaded capacitors are supplied with the same lead wire material, but the surface is not hot solder dipped, but is instead solder plated.

Question: What is the difference between military BX & BR, and how does it compare with commercial X7R, & X5R? How about military BP, as compared to commercial C0G, C0H, & C0K?
Answer: Military BX and BR are designations defining the maximum change in capacitance with respect to temperature and applied DC voltage.  

For the BX, the maximum allowable capacitance shift from nominal (25C and 0 VDC) is +15%/-25% over the range of -55C to +125C, with DC voltages of 0 & rated voltage.  The BR characteristic is similar, except that it allows a wider variation of +15%/-40%.  

Commercial X7R chips are rated over the full military range of -55C to +125C, with a maximum capacitance shift of +/- 15% over that range – BUT they do not have a requirement for maximum capacitance shift with voltage.  Due to the thinner dielectrics used for extended values in commercial chips, the capacitance shift with voltage may be considerably greater than that of military BX and BR.  Commercial X5R is similar to commercial X7R, but is rated over a lesser, non-military range of -55C to +85C.

Commercial C0G will meet the temperature/voltage capacitance stability requirements of military BP – but other construction and testing requirements will not be the same as the military products.  Commercial C0H and C0K (looser variations of C0G not offered by KEMET) will not meet the capacitance stability of military BP – they allow more variation of capacitance with temperature than does BP.

Question: Where are your military ceramic capacitors manufactured?
Answer: Military ceramic capacitors, both leaded and MLCC, are manufactured and tested at our plants in Monterrey, Mexico.

Question: What does “COTS” mean?
Answer: COTS stands for “Commercial Off The Shelf”, and indicates that this is a standard cataloged item with no outside drawing or specification requirements.  Click here to review the the Frequently Asked Questions for COTS.

Question: Can I order specially-screened military products? If so, why can’t I get “special” parts JAN branded?
Answer: JAN branding assures all products supplied against that military specification are manufactured the same way. Any additional testing could theoretically change the performance characteristics. Also, in a replacement situation, a “standard” military chip might not function properly as a replacement for the specially-screened unit. Thus, any specially-tested parts cannot be JAN branded. Nonetheless, KEMET can supply specially-tested ceramics without JAN branding, and specially-configured tantalums in our COTS program.

Question: Are military ceramics made with Base Metal Electrodes (BME)?
Answer: Military ceramics, both leaded and MLCC, are currently made only with PME (precious metal electrodes), rather than BME. This is not due to an issue with quality or reliability – instead, it is due to the fact that BME is a newer technology, which must be military qualified before it can be JAN branded. Indeed, BME parts have demonstrated excellent reliability and robustness in the commercial world, where they are used in many severe environments – including automotive.

Question: How can I determine the high frequency performance (capacitance, ESR, ESL, resonant frequency) of your military products?
Answer: High frequency performance can be determined by using our SPICE simulator, available for free download at our website.  As an added bonus, the SPICE simulator will also allow calculation of expected change in parametric performance for variations in temperature and applied DC voltage – both important factors in ceramic capacitor performance.

Question: What are the most significant differences in tantalum and ceramic capacitors for a given application?
Answer: Both tantalum and ceramic capacitors have advantages and disadvantages. The tantalum advantages are higher capacitance values within a given package size, stability of capacitance with applied DC voltage, and in surface mount configurations – resistance to flex-induced damage. The ceramic advantages are lower ESR, lower leakage, better high frequency performance, better resistance to transients and over voltages, and non-sensitivity to polarity.  A more detailed comparison is available in our KnowledgeEdge application on KEMET.com.

Question: What is the Moisture Sensitivity Level (MSL) of your military ceramic products?
Answer: Moisture Sensitivity Level (MSL) for surface mount components is based on J-STD-020. MLCC have an MSL of 1, since they have no plastic case or porous construction to entrap moisture. Leaded ceramic capacitors have not been characterized for MSL, since J-STD-020 applies to surface mount.

Question: What is the internal solder used in your leaded military ceramic products?
Answer: The internal solder on our leaded military ceramic capacitors (MIL-PRF-123, MIL-PRF-39014, MIL-PRF-20) is a high temperature alloy to minimize the possibility of internal reflow. The alloy used is 88Pb/10Sn/2Ag, with a solidus/liquidus of 268/290C.

Question: How can I calculate reliability for differing conditions of temperature and voltage?
Answer: Military product reliability calculations are generally based on the factors included in MIL-HDBK-217.       KEMET has developed a FIT Calculator based on MIL-HDBK-217, and this calculator can be used to determine reliability at differing conditions of temperature and voltage.  Review the FIT Calculator and download it on our FIT Calculator page.

Question: What is the flammability rating of your military ceramic capacitors?
Answer: MLCC:  Chips have been fired at high temperature, resulting in the removal of all organic compounds. In addition, they have no plastic case. As a result, they are not considered flammable.

Leaded:  All of the polymers used to encapsulate KEMET leaded ceramic capacitors have a UL flammability rating of 94V-0. The ceramic chips inside the case themselves are not flammable, as discussed under the MLCC topic above.

Question: Should I derate the DC voltage for ceramic capacitors, as I do for tantalums?
Answer: Ceramic capacitors have very high breakdown voltage in comparison to their rated voltage. This is due to the dielectric strength of their thick ceramic layers. Ceramic capacitors thus can withstand transients and over voltages that would damage an electrolytic capacitor, such as a tantalum. As a result, it is not necessary to derate the DC voltage for ceramics – you can operate at full nameplate voltage.

Question: Are your military ceramic capacitors subject to variations in performance due to changes in atmospheric pressure?
Answer: MLCC for surface mount are not susceptible to damage or electrical change due to varying levels of atmospheric pressure. They consist of a solid, fired block of ceramic and metals, which is resistant to any such conditions. In addition, leaded ceramics (contain an encapsulated MLCC) are also robust.

Question: Are your military ceramic capacitors subject to outgassing? Do they contain organic materials?
Answer: Ceramic MLCC:  These parts do not contain organic materials that can outgas.
Ceramic Leaded:  These parts are encapsulated in an epoxy case (contains organics), and can be subject to outgassing.

Question: Do your military ceramic capacitors exhibit “dielectric absorption”?
Answer: All military and commercial ceramic capacitors exhibit dielectric absorption, which is manifested as a spontaneous recovery of low levels of DC after previous charging and discharging.  There is more detailed information on dielectric absorption in a technical paper available from your KEMET representative.

Question: Do your military capacitors exhibit “aging”? If so, how is it quantized?
Answer:
Tantalum:  Tantalum capacitors do not exhibit aging.
Ceramic:  All military BX & BR dielectrics (similar to commercial X7R) exhibit aging, which is a linear decline in capacitance with the log of time.  Military BP dielectrics (similar to commercial C0G) do not exhibit aging, and remain stable with time.  There is more detailed information on aging in our KnowledgeEdge application on KEMET.com.

Question: What is the difference between military and commercial ceramic capacitors?
Answer: Both military and commercial ceramic capacitors share many similarities in construction, and testing.  However, military products are different in the following categories:

1.  Available Ratings:  Commercial products have a much larger selection of available ratings, since they can be supplied with the latest technology, including base metal electrodes (BME), high capacitance achieved through thin lower-voltage dielectric materials and higher layer counts, and additional case sizes and dielectric formulations.  
2.  Voltage Characteristic:  Military products are supplied against military designations of BX and BP, while commercial products are supplied against EIA designations of X7R and C0G (plus other non-military designations, such as X5R, Y5V, and Z5U.)  The military BX specifications include a voltage coefficient (change in capacitance with applied DC voltage) which is specified, while the similar commercial X7R specifications do not include this requirement.  
3.  Materials:  The military products have not yet been qualified for BME, so they continue to be supplied in PME (precious metal electrodes).
4.  Testing:  Military products require burn-in, plus other special tests.  Commercial products focus on in-line testing, rather than burn-in and other special testing.

For more specific information on the differences, particularly for MLCC versions,  KEMET has a brief technical paper – please request at our website or from your  salesperson.

Question: What are the termination types on military ceramic chips?
Answer: Military MLCC are available with either of two termination finishes. Our “Solderguard I” incorporates a Ni barrier layer to protect against leaching, with an over coating of Sn60 solder, applied by dipping. This termination meets the requirements of MIL-PRF-55681 “S” (solder coated, final), and “U” (base metallization – barrier metal – solder coated). For those customers requesting a plated termination, we offer “Solderguard II”, incorporating the same Ni barrier layer, which is then over-plated with pure matte Sn. This termination meets the current requirements of MIL-PRF-55681 “W” (base metallization – barrier metal – tinned or tin/lead alloy), or “Y” (base metallization – barrier metal – tinned – 100% Sn). In addition, we can supply gold plating over nickel, but this is considered a non-standard termination, and cannot be JAN branded.

Question: When will you offer case sizes 0603 & 0402 in military ceramic chips?
Answer: MIL-PRF-55681 does not currently include the 0603 and 0402 case sizes. However, DSCC is considering generation of new specifications for these parts, and KEMET is actively participating in the specification development. The new specifications will not be included as “slash sheets” in the current MIL-PRF-55681. In the meantime, customers can purchase non-JAN branded commercial chips.

Question: What is the difference between MIL-PRF-123 & MIL-PRF-55681
Answer: MIL-PRF-55681 is a standard military specification, with requirements for burn-in, maintenance of failure rate, and other electrical & environmental tests. MIL-PRF-123 is a “space grade” military specification, with more stringent burn-in requirements, plus additional requirements for testing and visual inspection.

Question: What about MIL-C-11015?
Answer: MIL-C-11015 is a special case – it is an “obsolete for new design” specification for non-established reliability leaded capacitors. It is essentially a commercial leaded capacitor.

Question: Can I substitute higher voltage and tighter tolerance ceramic capacitors in an application?
Answer: Substitution of higher voltage and/or tighter tolerance ceramics will work in essentially every application. Higher voltage parts will even result in greater reliability, due to the thicker dielectric, and to the testing protocol.

Question: Are your military MLCC available with physical standoffs?
Answer: At the present time, KEMET does not offer military MLCC with physical standoffs. However, we do offer a line of stacked MLCC on a lead frame, suitable for DC-DC converter applications.

Question: Are tin whiskers a concern for your ceramic military products?
Answer: Tin whiskers are a controversial topic.  Many of our military customers prefer terminations which are not pure Sn, and  KEMET offers parts in compliance with that preference.  Our MLCC are available with a solder-dip Sn60 termination finish, and our leaded ceramics are offered with solder-plated lead wires.  We do offer MLCC with matte Sn finish, and we have not seen any field problems with Sn whiskers.  Nonetheless, extremely small Sn whiskers can form on Sn-plated MLCC parts, particularly if the parts are used in bonding at low temperatures (below the 232C reflow point of Sn), or in epoxy-bonding applications.  KEMET presented a paper titled Whisker Evaluation of Capacitors Mounted with Lead Free Solders at the March 2004 IPC/JEDEC 5th International Conference on Lead Free Electronic Components and Assemblies.  For a copy of this presentation, please contact your salesperson or direct your question through KnowledgeEdge.

Question: Do your military products contain any of the Restriction of Hazardous Substances (RoHS) materials, including Cd, Pb, brominated flame retardants, etc.?
Answer: Military designers often demand finishes that contain Pb, and KEMET supplies these as required, although such lead finishes are not favored by RoHS restrictions.  There is also Pb in the internal construction of our leaded military products, as well as in the internal ceramic fired matrix of some of our ceramic chips.  However, this is allowed by RoHS.  Note that the molding compound on KEMET leaded military product does not contain the brominated flame retardants cited by RoHS.  More environmental information can be found at KEMET’s Green Product Roadmap.  

Question: What temperature profiles for soldering can your military ceramic products withstand?
Answer: Military MLCC are subject to the same recommendations by case size as are our commercial MLCC.  Technical papers on recommended soldering profiles for wave solder, reflow solder, and rework/touchup manual solder are all included on our website.  Soldering recommendations applicable to both leaded ceramic and tantalum capacitors can be found in our engineering bulletin for leaded tantalums, available at our website.

Question: What is the electrostatic dissipation capability of your ceramic products?
Answer: KEMET ceramic chips have high breakdown voltages, and are thus quite robust in most ESD type applications.  In some ESD testing, a simulator capacitor (typically either 150 or 200 pF) is charged to a high ESD voltage, and is then discharged into the capacitor under test.  Under such conditions, the final voltage seen by the capacitor under test is determined by charge redistribution between the two capacitors.  Thus, capacitors of very small value may be damaged by high ESD simulator voltages, since they can go as high as 25 KV.  More information on ESD capabilities is available in technical papers available on our website.

Question: Can your military products be used in Pb-free soldering profiles?
Answer: KEMET ceramic and tantalum surface mount capacitors can be used in Pb-free soldering profiles.

Question: What is the thickness of your military ceramic chips?
Answer: The thickness of our military MLCC meet the requirements of the applicable military specification. If more precision is required, please contact your salesperson with the exact part numbers required.

Question: Do you have military products that can be used at 150C?
Answer: While BX, BR, & BP characteristics can be used at 150C, we cannot test them under these conditions, due to JAN branding concerns. Note that the BX and BR parts will not have a defined temperature and voltage coefficient of capacitance at this elevated temperature, but they will still be useful in many applications. The BP characteristic will still be stable at a nominal of zero +/- 30 PPM/degree C.

Question: What is the flex capability of your military MLCC?
Answer: Flex robustness after soldering on the board is similar to that of commercial chips.   KEMET offers discussions of flex capabilities, and methods to reduce flex damage in technical papers downloadable at our website.

Question: How can I calculate DC leakage limits for your military ceramic products?
Answer: Ceramic capacitors have extremely low DC leakage (DCL), so insulation resistance (IR) is usually specified instead. If DCL must be determined, it is first necessary to calculate the IR. Do this by considering the IR limits in the catalog. For instance, the IR limit for many BX capacitors is 1000 megohm-microfarads, or 100K megohms, whichever is less. For a 0.1 uF capacitor, the IR limit would be 1000/0.1, or 10,000 megohms. To get DCL, we would divide the circuit voltage (say 10 volts) by the IR limit of 10,000 megohms to get 1/1000 microamp, or 1 nanoampere, a very small level of DCL.

Question: What is the “low voltage failure mode” and does it apply to military ceramics?
Answer: The "low voltage failure mechanism" has been the subject of much discussion over the years, but  KEMET has not seen this failure mechanism in our ceramic capacitors.  The primary method of checking for low voltage failure mechanism was the development of the low voltage humidity test, wherein low voltage is applied through high impedance in a humid environment, followed by insulation resistance checks, again at low voltage and high impedance.  The test has long been formalized in the military chip specification, MIL-PRF-55681, as part of the group C test schedule.  There is no corresponding test in MIL-PRF-39014, the leaded military specification.

However, the ceramic chips we use in MIL-PRF-55681 are manufactured using the same dielectric and electrode materials as those in MIL-PRF-39014.  Additionally, the dielectric thicknesses follow the same guidelines for the 50 volt ratings.  Thus, the low voltage humidity data collected for MIL-PRF-55681 could be used to predict MIL-PRF-39014 performance.

To date, we have never experienced a failure in the MIL-PRF-55681 due to the low voltage humidity phenomenon, so we are skeptical about the possibility of "low voltage failure mechanism"  for  military ceramic products.  It is true that high capacitance (high layer count), coupled with low voltage (thinner dielectric), can make parts more susceptible to failure on life testing, but this does not convince us of the existence of any special physical phenomena such as "low voltage failure mechanism".

Question: What are the typical failure modes of your military capacitors? Can they ignite or burn?
Answer: The typical failure mode of ceramic and tantalum capacitors is the short circuit.

Tantalum: Certain types of electrolytic capacitors, such as some tantalum types, use metallic slugs or foils, which can ignite in the presence of high temperature (as from a fault current in overstress) and in the presence of oxygen (typically supplied by overheated counter-electrode material, such as MnO2).  However,  also offers a surface mount tantalum (our organic “KO”)  that is  quite resistant to such ignitions.  These parts use an organic polymer as the counter-electrode, which reduces the fault current and also does not release oxygen.  Additionally,  KEMET offers a line of SMT tantalums which incorporate an integral fuse, which changes the failure mode from short circuit to open circuit.

Ceramic MLCC:  Ceramic MLCC’s do not ignite or burn in the traditional sense, since the ceramic chip does not contain materials capable of igniting in use.  However, an MLCC can be damaged (flex cracks, thermal shock cracks, mechanical impact cracks, dielectric flaws), and this can allow the passage of large current levels, particularly in a low impedance, moderate voltage application.  Under such circumstances, localized fault current can flow, causing joule heating at the fault site.  This focused current can cause high temperatures at the fault site, and this can result in fracture, along with melted ceramic and metal components.  While the capacitor chip does not ignite, the heat can ignite the underlying glue dot in cases of SMT mounting.  In extreme cases, the capacitor may explosively rupture.  In the case of selected SMT chips, it is possible to reduce the probability of the most common failure cause - flex cracks - by using a specially designed "flex-open" chip, which changes the characteristic short-circuit flex failure mode to an open-circuit.  Once again, you can contact KEMET Sales to learn more about these parts.

Ceramic Leaded:  These products can suffer a short through the failure mechanism described under “Ceramic MLCC”.  In addition, they may experience dendritic growth if board assembly techniques promote the ingress of flux and other ionic products.  Dendrites are encouraged by the presence of moisture, ionic materials, voltage, and time.  The most common root cause is a radial leaded part inserted with the conformal coating down into the hole.  In such cases, multiple factors can drive the board assembly flux up into the capacitor assembly where it promote the formation of dendrites.  The factors include the type of flux (chemistry of activator, wetting ability/surface tension), the amount of conformal coating down in the hole (where the flux can wick up if the epoxy is cracked or damaged), and most importantly - the wash method (where high pressure or high temperature, coupled with contamination of the wash solution, can result in flux ingress.)

Question: Are your military ceramic capacitors subject to the piezoelectric effect?
Answer: Certain classes of ceramic capacitors exhibit a normal characteristic, called piezoelectricity, than can cause unexpected effects in certain circuits.  In some cases, the piezoelectric effect may result in the appearance of electrical noise, while in other cases, an acoustic sound may be heard, coming from the capacitor itself.  Ceramic piezo effects are well known, and were even the basis for the ceramic phono cartridges used in the past.

Piezoelectricity is a common characteristic of many ceramic chip capacitors and occurs in those classes of dielectric which are classified as ferroelectric.   Piezoelectric effects can result in noise for ferroelectric ceramic chips, such as those used for military BX & BR, as well as commercial EIA Class 2 and Class 3 dielectric, such as X7R, X5R, X8R, Y5V, Y5U, Z5U, etc.  Piezoelectricity occurs in all ferroelectric dielectrics, regardless of manufacturer.  Note that there are essentially no piezoelectric effects in Class 1 capacitors, such as C0G, NP0, or military BP - none of which are ferroelectric.  

Piezoelectric noise is only occasionally an issue, since it is low level.  However, it can show up in specialized applications subject to mechanical stress of the ceramic during shock, vibration, compression, and torsion.  Examples include high gain pre-amps, hand-held microphones at rock concerts, and  monitoring equipment subjected to sudden shock or heavy vibration.  When it occurs, most piezoelectric noise is in the 3 KHz to 30 KHz ranges, although detailed studies have not been done over a wider range.

The piezoelectric effect is tied to the crystal structure of the dielectric.  In ferroelectric materials, the crystal structure tends toward the tetragonal, with the Ti cation located at a non-centered position in the crystal.  This results in an electric dipole structure.  When this structure is mechanically deformed, the charge center of the crystal shifts, producing a dipole moment and polarization.  This results in the appearance of a voltage at the capacitor terminals.  That voltage increases as the mechanical deformation increases.  This can be a design issue in high gain amplifier circuits subject to mechanical vibration or sudden impact, since these piezoelectric voltages could be coupled into the circuit, introducing errors.

The complementary effect also occurs, in that electrical stimulation of ferroelectric compounds can result in mechanical deformation.  In circuits which operate at acoustic frequencies, the capacitors will tend to respond and may emit acoustic noise.  As the frequency goes up, the capacitor can no longer respond, and the acoustic noise will be damped out

Remedies depend upon the operating constraints of the designs.  Use of a different capacitor type is one obvious approach, and may be the only solution for low frequencies.  Other possibilities include (must be evaluated by the customer, based on circuit requirements):

• Use a different dielectric - C0G can replace X7R for low cap values, if the package size increase  is acceptable.
• Use a different type of capacitor, such as tantalum (the 1206 0.1 uF 50 volt ceramic can sometimes be directly replaced by a tantalum equivalent, the 3216.
• Use a leaded part, rather than SMT - the leads tend to decouple the mechanical stress from the chip
• Use a smaller footprint SMT part, to minimize the span on the board, which can help to isolate the chip from flex and vibration effects
• Minimize vibration on the board by changing the board mount system, adding dampening materials near the chip, or by relocating the chip.
• Use a part with thicker dielectric, usually corresponding to a higher voltage rating.  This reduces the voltage gradient, which reduces piezoelectric noise, if the package size increase  is acceptable.
• Use a chip with greater overall thickness, which helps to prevent physical distortion and stress.